1. Field of the Invention
The present invention relates to an intake structure of a motorcycle, which may be referred to as a layout of an intake device or merely an intake device.
2. Description of the Related Art
A conventional intake structure or device of a motorcycle includes an electronically controlled throttle that drives a throttle valve by means of an electric motor to thereby adjust a flow rate of intake air.
A throttle body of such electronically controlled throttle partitions a throttle bore as a flow path that guides intake air from an air cleaner box to an engine. The throttle valve is a valve acting to open and close the throttle bore.
The electronically controlled throttle measures an operation amount of a throttle grip by an accelerator position sensor and determines a control amount of the electric motor, i.e., an opening degree of the throttle valve.
Such an intake structure of a motorcycle in which the accelerator position sensor is arranged outside a main frame is known (for example, refer to Patent Document 1 (Japanese Patent Laid-Open Publication No. 2008-274925)).
The accelerator position sensor measures the operation amount of the throttle grip by measuring a rotation angle of a throttle pulley around which a cable extending from the throttle grip is wound.
According to such arrangement, there may case a possibility in which the throttle pulley is vibrated by vibrations generated during the running of the motorcycle or vibrations generated by the engine, leading rotation of the throttle. As a result, the accelerator position sensor may be erroneously operated and incorrectly measure the operation amount of the throttle grip.
On the other hand, in an adoption of a layout or arrangement in which the accelerator position sensor is located outside the main frame, an outer appearance of a motorcycle is not good and may be easily damaged, particularly, in a so-called naked-type motorcycle having a few exterior parts or components, or a so-called sports-type motorcycle having an exposed main frame, thus being inconvenient.
In the meantime, the motorcycle of the conventional type having an intake structure or device such as mentioned above also includes an engine having a forward inclined cylinder axis and an air cleaner box disposed above (or immediately above), and a fuel tank disposed on a rear side of the air cleaner box.
In such arrangement of a conventional motorcycle, a throttle body is generally arranged in a position on a back surface side of the forward inclined engine or a recessed portion of a lower surface of the air cleaner box, and an electric motor is positioned rearward downward apart from the throttle body (for example, refer to Patent Document 2 (Japanese Patent Laid-Open Publication No. 2002-129987)).
There is also known a motorcycle in which an electric motor is arranged in a manner sandwiched between a head cover of an engine and an air cleaner box (for example, refer to Patent Document 3 (Japanese Patent Laid-Open Publication No. 2010-223004).
In such conventional motorcycle, there was adopted an arrangement in which, in order to protect an electric motor of an electrically controlled throttle from heat generated by an engine, and to ensure a volume of a fuel engine, the electric motor is arranged below the throttle body and a throttle valve and the electric motor is connected by means of wire cable. In order to realize such arrangement, it is required for the conventional motorcycle to be provided with considerably large area for disposing the throttle valve and the electric engine. On the other hand, even if such area is minimized, there requires countermeasure against generated heat to the electric motor.
In addition, conventional technology has provided another conventional motorcycle in which an electric motor is arranged in a manner sandwiched between the head cover and the air cleaner box to thereby improve degree of freedom for the layout around the cylinder of the engine. However, in order to ensure an area for arranging the electric motor therebetween, it is required for the air cleaner to have a small-sized structure, leading difficulty for ensuring sufficient area for disposing the air cleaner box.